Fields of the Disclosure
The present disclosure relates to a double walled thermal glass, cup, or other container with improved reliability.
Related Art
Double walled glasses and cups are produced in large quantities to provide thermal insulation for hot and cold drinks. These vessels are commonly molded using clear, high luster plastic materials such as polycarbonate, for example, and then sonic welded together to form a seal between the inner liquid containing chamber and the outer covering chamber. The area between the inner container and the outer housing provides thermal insulation between the inside and outside of the container. Stress cracking in the interface of the welded seal, however, leads to reliability problems. After continued usage or washing, especially in dishwashers with a hot dry cycle, stress fractures are common. Even a small crack may allow thermal cycle pumping of moisture into the area between the inner and outer containers. This reduces the insulation provided by this area. Further, the moisture condenses to provide a cloudy appearance which may interfere with viewing or damage artwork or other indicia typically provided in this area for decoration. The use of more costly and attractive inner container artwork is thus prohibited due to future failure replacement costs.
Accordingly it would be beneficial to provide a double walled thermal container that avoids these and other problems.